Meet Raptorex, the amazing miniature T. rex

In northeastern China, the fossil of a new dinosaur, named Raptorex kriegsteini that lived 125 million years ago has been uncovered.

The Raptorex had an oversized head with powerful jaws for biting, long legs for running and tiny arms that did nothing – it was basically an earlier version of Tyrannosaurus rex, who lived 35 million years later.

The Raptorex, however, was about the size of a human.

The scientists are sure that the new mini tyrant is not just a juvenile. Bones in animals tend to fuse in sequence, providing a key to an animal’s maturity level.

Raptorex’s pelvic girdle was completely fused and its scapula and shoulder blade were nearly so, indicating that it was an adolescent at the end of its growth. [Wired]

The stunted arms of T. rex has previously been thought by many to have evolved has a consequence of T. rex being so big. But the Raptorex shows that the basic body plan of T. rex was already present in its earlier ancestors – it just got bigger.

But why the big head and small arms? Paleontologist Paul C. Serano tells the New York Times:

Raptorex, like T. rex, would have killed animals with its teeth and jaws. The forelimbs would not have been the primary means for attacking prey.

In fact, Dr. Sereno said, the forelimbs would have gotten smaller as the head got larger. “This is an agile, fast-running animal,” he said.

“By adding a lot of weight at the top, something has to give way. What gave way was the forelimb.”